Subsea pipelines are conventionally used for transporting fluid such as gas or oil from a well to a platform/template or the like. When the transporting process is operative the pipeline wall is heated by the hot (150 to 200 degrees C.) flowing fluid. The pipeline wall will during this phase obtain its maximum elongation.
When the transport of fluid has to be stopped—for some reason or other—the fluid within the pipeline wall will gradually cool down to the temperature of the surrounding sea (some 4 degrees C.) resulting in clogging of the pipeline by hydrate formation of the fluid. During this phase, the pipeline will contract and experience its minimum elongation. Before reaching this phase it is well known to heat the pipeline sufficiently to prevent the mentioned clogging of the fluid within the non-operated pipeline using an electrical heating system.
To this purpose, the heating system comprises a subsea electrical cable clamped to the pipeline surface at more or less regular intervals, in parallel to the pipeline axis. During this installation, the subsea electrical cable is submitted to pulling forces—typically around 20 kN—so that it becomes a tensioned cable. Moreover, whereas the pipeline is quite capable of expanding and contracting—in the axial direction—as a result of temperature changes,—this is not so with the clamped subsea electrical cable. Forced into the same elongation during production, typical tension in the subsea electrical cable will be increased from 20 kN to 120 kN approximately. But such a high tension is unpredictable, and beyond what is acceptable for the cable itself and the cable clamps. The clamps will therefore break or move relatively to the subsea electrical cable and the pipeline and in worst case, damaging both.